The present invention relates to improvements in assemblies which are used to take up and to compensate for shocks which develop as a result of fluctuations in the rotational speed of flywheels or other rotary parts. More particularly, the invention relates to improvements in assemblies which can be used with advantage in internal combustion engines to take up and compensate for fluctuations in torque of at least two coaxial parts which are rotatable, within limits, with reference to each other. Still more particularly, the invention relates to improvements in assemblies which can be used in internal combustion engines to resist rotation of two parts of a flywheel relative to each other, especially relative rotation of two parts one of which receives torque from the engine and the other of which transmits torque to the input element of a change-speed transmission in a motor vehicle.
Assemblies of the above outlined character are disclosed, for example, in German Offenlegungsschrift No. 2 926 012. The damping action between two rotary parts which can move (within limits) angularly with reference to each other is furnished by energy storing devices in the form of coil springs and by a friction generating unit which operates in parallel with the coil springs. The arrangement is such that the coil springs offer a progressively increasing resistance to further angular displacement of the two parts relative to each other from a neutral or starting position. Thus, the coil springs will yield rather readily when one of the parts begins to change its angular position relative to the other part, and such resistance increases progressively with increasing angular displacement of the one part relative to the other part. At the same time, the resistance of the friction generating device, which operates in parallel with the coil springs, remains at least substantially unchanged.
Assemblies which embody the just discussed damping devices operate in such a way that their critical fundamental frequency, i.e., the critical RPM of the driven and driving parts, develops at a resonance which is below the ignition cycle frequency when the RPM of the engine is at a minimum value, i.e., the lowest RPM at which the engine is still in operation. However, when an internal combustion engine is started or turned off, it often takes a reasonably long interval of time during which the RPM is within the critical range so that the vibration amplitude of the two parts which are rotatable relative to each other increases still further as a result of excitation within such range of rotational speeds. These high-amplitude vibrations generate alternating torque of such magnitude that the damping system between the two parts undergoes maximum deformation and acts as a rigid link between the two parts. In other words, the damping device then ceases to take up and/or compensate for torsional stresses and simply acts as a solid anvil which is struck by or strikes against the two parts. The resulting shocks not only affect the comfort of the operator and occupants of the vehicle but they also generate readily detectable noise and shorten the useful life of the connection between the engine and the transmission, of various bearings, of shafts and other parts in the motor vehicle.